Engineering problems are often characterized by many conflicting objectives which span over several engineering domains. In this paper an approach to design of objective functions for engineering problems is presented. Multi-domain systems can be characterized as complex systems which combine different fields of engineering. Here an aircraft landing gear is studied which is a true example of a multi-domain simulation problem due to the presence of mechanical, electrical and hydraulic sub systems. On this simulation model a non-gradient optimization strategy is applied where the formulation of the objective function is supported by the House of Quality method. The design of an objective function for optimization is in many cases a complex procedure involving a great amount of expertise. The House of Quality method is used here both to facilitate team activities and to elucidate the relation between system characteristics and system parameters.